Police investigating suspicious break-ins of a prominent China researcher appear to have initially put the case on ice with a low priority and before the Prime Minister's public concerns this week saw the file thawed.

Last week the Herald broke news that University of Canterbury professor Anne-Marie Brady's home was burgled, and she told an Australian parliamentary committee she believed the break-in was linked to her work detailing China's influence campaign in New Zealand.

Brady disclosed computers, phones and USB drives were taken during the burglary last week of her Upper Riccarton home, and the event followed a similar intrusion at her campus office in December and the recent receipt of an anonymous letter warning she was being targeted by pro-Beijing interests.

A letter dated Monday sent by Christchurch police to Brady about the case said investigating officers had no leads and the matter was being sent to the Canterbury file management centre.

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"After looking at all the available evidence we have not been able to find out who is responsible .... Unless more information or evidence is found, we can't proceed any further with this case," the letter said.

But yesterday a police spokesman, presented with the letter, sought to clarify matters: "These matters are ongoing and continue to be under investigation."

The apparent about-face followed Prime Minister Jacinda Ardern expressing concern at the Herald report at her post-Cabinet press conference on Monday, and requesting a briefing on the matter from the New Zealand Security and Intelligence Service.

Yesterday morning on RNZ Ardern restated her concern over the Brady case and noted she would be in touch with agencies probing the matter.

"The police obviously are completing their investigation – and I see they're seeking the room and space to do that before drawing any conclusions," she said.

Careful not to single out China by name, Arden said: "Foreign interference does come from a range of sources, and we should be wise to every source and make sure we're doing all we can to protect ourselves from that."

Australia's Clive Hamilton, an academic at Charles Sturt University, said the Brady case was being "closely followed" by China researchers internationally because she was a well-regarded voice in academia and the burglaries were "very disturbing".

"She has been very courageous in speaking out about the nature and extent of PRC [People's Republic of China] influence in New Zealand," he said.

"She deserves the support of the New Zealand Government, because she is pointing out some very important truths."

Hamilton said he had faced pressures of his own related to his research, including seeing three prospective publishers of his upcoming book on China's influence in Australia withdraw their involvement "citing the fear of retaliation by Beijing".